This invention relates generally to the field of mobile refrigeration units, and more particularly to a mobile refrigeration unit that undergoes a process whereby a service technician can service the low pressure side.
The purpose of a low side pump down is to provide service technicians with an opportunity to service the low pressure side of a mobile refrigeration system. Examples of the types of service which can be performed include replacing the filter dryer, replacing or servicing the electronic expansion valve, the electronic modulation valve, the compressor suction pressure transducer, and the compressor suction temperature thermistor. Service can be performed after the refrigerant is removed from the system, which is a costly and lengthy process. Alternately, the service technician can engage in a tedious manual process, consisting of attaching gauges to the system at appropriate locations, closing the shut-off valve, watching the suction pressure, shutting off the unit when a specified low suction pressure is achieved, watching the gauges again to monitor the suction pressure, and if the suction pressure begins to rise, running through the process again. Eventually, the technician is able to service the low pressure side.
Briefly stated, a microprocessor controlled system performs low pressure side pumpdown with the assistance of a service technician. When the refrigerant in the system is transferred to the high pressure side, the low pressure side is available for servicing by the technician.
According to an embodiment of the invention, an apparatus for low pressure side pumpdown processing of refrigerant in a mobile refrigeration unit includes a compressor; an engine which powers the compressor; a microprocessor connected to the engine and to a plurality of valves and sensors in the unit; means, responsive to the microprocessor, for minimizing an amount of refrigerant mixed with oil in the compressor; and transferring means, responsive to input from a user, for transferring substantially all of the refrigerant from a low pressure side of the unit to a receiver.
According to an embodiment of the invention, a method for low pressure side pumpdown processing of refrigerant in a mobile refrigeration unit includes the steps of providing a microprocessor connected to a plurality of valves; providing a compressor for the unit; minimizing an amount of the refrigerant mixed with oil in the compressor; opening and closing specified ones of the plurality of valves; running, in response to the microprocessor, a compressor to pump refrigerant in the unit into a receiver; monitoring a suction pressure and providing results of the monitoring to the microprocessor; shutting down the compressor, in response to the microprocessor, after the suction pressure falls below a first predetermined point; opening, in response to the microprocessor, an electronic evaporator expansion valve and monitoring the suction pressure to see if the suction pressure remains below a second predetermined point; signaling the microprocessor to resume normal operation; and opening and closing, in response to the microprocessor, specified ones of the plurality of valves to return the unit to normal operation.